Cassima states a desire in the opening (separate from the gameplay) scene: "Oh Alexander, I wish you were here!" But I think you're right: she has nothing to "move" her, because she serves as Alexander's ultimate goal.  (Actually, the only entity who serves as another's specific desire - the Beast wants "a princess", the Black Widow wants "a husband/meal", but neither of them are picky.) Cassima is the most stationary character, while Alexander is the most mobile. More than the tinderbox or the flute, he really has to know where she is all times. It was actually a really creepy moment to me in the last playthrough when Alexander talks to Cassima through the door and asks, "Do you want me to let you out?" Of course she wants to be let out - what kind of question is that?! And THEN she said something like "Oh, no, I'm safe right here. For now." My jaw dropped. Maybe they're perfect for each other.